熊猫Python新列数据框

Question

I have problems with initializing a new column in a dataframe, called df I want to do:

df['new_column'] = 0

to have all values to zero..

But then is gives me:

A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead

.. so, when I then want to work on it it **** up...

I looked up on the net but didn't really find something useful.. I am a beginner in pandas so sorry if the answer is obvious but I really don't know how to do this basic thing..

Thanks!

Answer 1

I'm guessing this is because your df is already a view on some other dataframe like:

df = DF.iloc[100:]

in this case pandas will not really copy the data but just keep a reference to the old one. In my mind this is not very transparent and I have shot myself in the foot a couple of times with that.

a work around is to enfoce a copy of the dataframe to be sure it owns its own data:

df = df.copy()

so in your case you might want to do:

df = df.copy()
df['new_column'] = 0

I hope that does the trick for you